The practice of treating seeds or other plant propagation material with pesticide formulations is well known. The pesticide formulation should not harm the seeds, be stable for relatively long periods of time before planting, adhere well and evenly to the seeds, be compatible with planting equipment, and be relatively inexpensive.
Insecticides and fungicides are applied to seeds to protect them from pests throughout their life cycle, but seed treatments are especially effective for protecting the plants from pests prior to and during germination, and in the seedling stage. Seed treatment formulations can be dusts, slurries or liquids. Two common liquid seed treatment formulations are dispersible concentrates and flowable concentrates for seed treatments.
A variety of pesticidal agents are insoluble or not readily soluble in water. To overcome this problem, seeds can be treated with formulations such as wettable powders, dry flowables, emulsifiable concentrates and other similar single-phase formulations that are mixed with water by the user prior to application. These types of formulations have several disadvantages including dusting during handling (possibly causing injury to the user and the nearby environment), inhomogeneous mixing by the user (resulting in uneven pesticide distribution), and settlement or clogging of spray tank screens during application. These formulations also have the disadvantage of requiring agitation or further mixing during application. Further, these formulations may require milling which can significantly increase manufacturing costs.
A dispersible concentrate (DC) is a liquid formulation that is applied as a solid dispersion after dilution in water. A water miscible organic fluid, or a mixture of multiple fluids, is usually used to dissolve water-insoluble or partially soluble pesticidal agents. After dilution in water, the pesticidal agents precipitate out and disperse as micronized solid particles as the carrier fluid is dissolved in water. Dispersible concentrates contain surfactants that make a uniform and stable dispersion of the precipitated solid particles. The formulation may include water as long as the liquid mixture maintains sufficient solubility of the pesticidal agents in it. Furthermore, DC formulations may contain other ingredients that function in various ways either in the formulation itself or when it is diluted with water, or when the product is applied on to seeds or other plant propagation materials. These ingredients include compatibility agents, stickers, film formers, slip agents, colorants, etc. These additives may not be dissolved but dispersed in the carrier liquid; therefore, the DC may not always look homogeneous. By choosing the appropriate organic fluids, the pesticidal active ingredients can remain physically and chemically stable for an extended period of time, ensuring a long shelf life for the product.
It is known that stable aqueous suspension concentrate formulations are not easily obtained for certain pesticidal agents that have relatively higher water solubility and/or lower melting point. For example, metalaxyl (mp 63-72° C. for the technical grade, water solubility 8400 ppm) is one such compound. Obtaining stable aqueous suspension formulations of metalaxyl is very challenging because it is difficult to prevent the compound from re-crystallizing and causing physical instability during storage.
Besides the storage concerns, dispersible concentrates typically cannot be used as a seed treatment. Conventional dispersible concentrates contain solvents that reduce the germination rate of the seeds and therefore are not desirable for application to seeds.
Further, obtaining stable formulations that are safe for seeds and effective requires the formulator to decide on the presence or absence of many inert additives. There are hundreds of options for some types of additives. The art of creating formulations with the desired characteristics by picking the precise components and their precise amounts is unpredictable. Often slight changes in amounts or substitutions of additives result in a formulations with entirely different characteristics that one skilled in the art would expect. Extensive experimentation is sometimes needed to prepare desirable formulations. Formulating pesticides for seed treatments involves knowledge of the thermodynamics of mixing, phase equilibria, solutions, surface chemistry, colloids, emulsions and suspensions, among other things.
Fungal infections are a major concern for crop growers. Fungi can be present on the seed surface prior to planting, they can be soil-borne, or they can be introduced into the growing environment by mobile pests or equipment. Fungi infect seeds and seedlings and destroy plant cells and tissues and thereby prevent seed germination or cause poor development or death of seedlings. Aphanomyces, Fusarium, Helminthosporium, Pythium, and Rhizoctonia are all known to cause infection and death of plants. These organisms cause seed rot, damping-off, seed blight, and root rot. Diseases that affect adult plants can also be controlled by pesticidal seed treatments (e.g., smuts caused by Ustilago, Tilletia, and Urocystis).
There remains a need in the art for a dispersible concentrate formulation that readily dissolves the pesticidal agent, maintains physical and chemical stability during long-term storage under environmentally stressful conditions, and exhibits excellent seed protection. There also remains a need in the art for a dispersible concentrate formulation that readily mixes with flowable concentrates for seed coatings. Furthermore, there is a need in the art for a dispersible concentrate that is easily diluted by an end user to prepare a seed treatment that provides improved protection against fungal pests.